C 程序没有从我给它的“正确”输入中给出所需的输出

Question

I am reposting this because my previous post was closed down due to improper formatting; hopefully that's fixed.

When I give it the correct input which is an IPv4 with the submask of 8, 16, 24, or 32, it does nothing and still takes in input when I press enter, whilst it obviously should return an output of the broadcasting IP's. What am I doing wrong in the following code that I'm getting this error? I have tried debuggers but none of them are helping me solve the issue so far. This is for an assignment, and the usage of Arrays is not allowed.

#include <stdio.h>

int IPAndSubnetMaskInput(int IPAndSubnetMaskFirstOctate, int IPAndSubnetMaskSecondOctate, int IPAndSubnetMaskThirdOctate, int IPAndSubnetMaskFourthOctate, int IPAndSubnetMaskSubnetInput) {

    printf("Please input an IPv4 address followed by the subnetmask (must either be 8, 16, 24, or 32) in the following format: 192 168 1 1 32: \n"); //Statement to ask for IP and submask input and puts the inputs into a variable to calculate Broadcast IP

    int IPv4AndSubmask = scanf("%d %d %d %d %d", &IPAndSubnetMaskFirstOctate, &IPAndSubnetMaskSecondOctate, &IPAndSubnetMaskThirdOctate, &IPAndSubnetMaskFourthOctate, &IPAndSubnetMaskSubnetInput); //Input function

    while (!(IPAndSubnetMaskSubnetInput == 8 || IPAndSubnetMaskSubnetInput == 16 || IPAndSubnetMaskSubnetInput == 24 || IPAndSubnetMaskSubnetInput == 32)) { //Initializing loop to evaluate whether subnet is correct or not

        printf("Your submask is wrong. Please enter a value that's either 8, 16, 24, or 32: \n");
        IPAndSubnetMaskSubnetInput = scanf("%d", &IPAndSubnetMaskSubnetInput);

        if (IPAndSubnetMaskSubnetInput == 8 || IPAndSubnetMaskSubnetInput == 16 || IPAndSubnetMaskSubnetInput == 24 || IPAndSubnetMaskSubnetInput == 32)
        {
            break;
        }
    }

    return IPv4AndSubmask;//function returns the value of IP octates and the subnet mask for the program to calculate
}

int broadcastCalculator(int broadcastFirstOctate, int broadcastSecondOctate, int broadcastThirdOctate, int broadcastFourthOctate, int broadcastSubnetInput) { //Declaration of first function for first Assignment point
    IPAndSubnetMaskInput(broadcastFirstOctate, broadcastSecondOctate, broadcastThirdOctate, broadcastFourthOctate, broadcastSubnetInput);

    while (0 == 0) {

        if (broadcastSubnetInput == 8) { //Conditional statement for submask of 8
            printf("The broadcast IP is:\t%hhu\t%hhu\t%hhu\t255\t\n", broadcastFirstOctate, broadcastSecondOctate, broadcastThirdOctate);//Program will print the Broadcast IP of firstOctate  secondOctate thirdOctate 255
            break;
        }
        else if (broadcastSubnetInput == 16) {//Conditional statement for submask of 16
            printf("The broadcast IP is:\t%hhu\t%hhu\t255\t255\t\n", broadcastFirstOctate, broadcastSecondOctate);//Program will print the Broadcast IP of firstOctate  secondOctate 255 255
            break;
        }
        else if (broadcastSubnetInput == 24) {//Conditional statement for submask of 24
            printf("The broadcast IP is:\t%hhu\t255\t255\t255\t\n", broadcastFirstOctate);//Program will print the Broadcast IP of firstOctate  255 255 255
            break;
        }
        else if (broadcastSubnetInput == 32) {//Conditional statement for submask of 32
            printf("The broadcast IP is:\t255\t255\t255\t255");//Program will print the Broadcast IP of 255  255 255 255
            break;
        }
    }
    return 0;
}


int main()

{
    int FARfirstOctate = 0; int FARsecondOctate = 0; int FARthirdOctate = 0; int FARfourthOctate = 0; int FARsubnetInput = 0;
    broadcastCalculator(FARfirstOctate, FARsecondOctate, FARthirdOctate, FARfourthOctate, FARsubnetInput);

    return 0;
}

Answer 1

There are several problems in your code! The first (and most serious) error is that you are passing values by value - which will mean the functions receive "copies" of the data, and cannot change the values in the calling code. To fix this, you need to declare the arguments as pointers and pass the addresses of the variables to change.

Another problem that you have (in a few places) is that you are assigning variables the return value of the scanf function: this is wrong , as that will be the count of how many values were (successfully) read by scanf .

Here's a 'fixed' version of your code, with triple-slash comments (///) added with notes where I've made changes:

#include <stdio.h>

/// Declare the arguments as POINTERS - so we can change the values in the calling code ...
int IPAndSubnetMaskInput(int* IPAndSubnetMaskFirstOctate,
                         int* IPAndSubnetMaskSecondOctate,
                         int* IPAndSubnetMaskThirdOctate,
                         int* IPAndSubnetMaskFourthOctate,
                         int* IPAndSubnetMaskSubnetInput)
{
    printf("Please input an IPv4 address followed by the subnetmask (must either be 8, 16, 24, or 32) in the following format: 192 168 1 1 32: \n"); //Statement to ask for IP and submask input and puts the inputs into a variable to calculate Broadcast IP

    /// This line WAS WRONG - the return value from scanf is the COUNT of values read!
    int IPv4AndSubmask = 0; /// We need to do something here to get a meaningful return value
    scanf("%d %d %d %d %d", /// As they are ALREADY pointers now, we don't need the addresses ...
        IPAndSubnetMaskFirstOctate,
        IPAndSubnetMaskSecondOctate,
        IPAndSubnetMaskThirdOctate,
        IPAndSubnetMaskFourthOctate,
        IPAndSubnetMaskSubnetInput); //Input function

    while (!(*IPAndSubnetMaskSubnetInput == 8 ||  /// As they're now all POINTERS, we need to dereference them...
             *IPAndSubnetMaskSubnetInput == 16 ||
             *IPAndSubnetMaskSubnetInput == 24 ||
             *IPAndSubnetMaskSubnetInput == 32))
    { //Initializing loop to evaluate whether subnet is correct or not

        printf("Your submask is wrong. Please enter a value that's either 8, 16, 24, or 32: \n");
        /// This line is WRONG - the return value from scanff is the COUNT of values read!
    //  IPAndSubnetMaskSubnetInput = scanf("%d", IPAndSubnetMaskSubnetInput);
        scanf("%d", IPAndSubnetMaskSubnetInput); /// Already a pointer!

     /// We don't need this check - the loop will exit when the condition is matched!
     //   if (*IPAndSubnetMaskSubnetInput == 8 || /// As they're now all POINTERS, we need to dereference them...
     //       *IPAndSubnetMaskSubnetInput == 16 ||
     //       *IPAndSubnetMaskSubnetInput == 24 ||
     //       *IPAndSubnetMaskSubnetInput == 32)
     //   {
     //       break;
     //   }
    }
    return IPv4AndSubmask;//function returns the value of IP octates and the subnet mask for the program to calculate
}

/// Declare theargumetns as POINTERS - so we can change the values in the calling code ...
int broadcastCalculator(int* broadcastFirstOctate,
                        int* broadcastSecondOctate,
                        int* broadcastThirdOctate,
                        int* broadcastFourthOctate,
                        int* broadcastSubnetInput)
{ //Declaration of first function for first Assignment point
    IPAndSubnetMaskInput(broadcastFirstOctate,
                         broadcastSecondOctate,
                         broadcastThirdOctate,
                         broadcastFourthOctate,
                         broadcastSubnetInput);
    while (0 == 0) {
        /// As before, we now need to DEREFENCE the pointers...
        if (*broadcastSubnetInput == 8) { //Conditional statement for submask of 8
            printf("The broadcast IP is:\t%hhu\t%hhu\t%hhu\t255\t\n",
                *broadcastFirstOctate,
                *broadcastSecondOctate,
                *broadcastThirdOctate);
            //Program will print the Broadcast IP of firstOctate  secondOctate thirdOctate 255
            break;
        }
        else if (*broadcastSubnetInput == 16) {//Conditional statement for submask of 16
            printf("The broadcast IP is:\t%hhu\t%hhu\t255\t255\t\n",
                *broadcastFirstOctate,
                *broadcastSecondOctate);
            //Program will print the Broadcast IP of firstOctate  secondOctate 255 255
            break;
        }
        else if (*broadcastSubnetInput == 24) {//Conditional statement for submask of 24
            printf("The broadcast IP is:\t%hhu\t255\t255\t255\t\n",
                *broadcastFirstOctate);
            //Program will print the Broadcast IP of firstOctate  255 255 255
            break;
        }
        else if (*broadcastSubnetInput == 32) {//Conditional statement for submask of 32
            printf("The broadcast IP is:\t255\t255\t255\t255");
           //Program will print the Broadcast IP of 255  255 255 255
           break;
        }
    }
    return 0;
}

int main()
{
    int FARfirstOctate = 0; int FARsecondOctate = 0; int FARthirdOctate = 0; int FARfourthOctate = 0; int FARsubnetInput = 0;
    broadcastCalculator(&FARfirstOctate, &FARsecondOctate, &FARthirdOctate, &FARfourthOctate, &FARsubnetInput);
    return 0;
}

Feel free to ask for further clarification and/or explanation.

Answer 2

Your code has some problems:

• You are passing integers by parameters. Those values are getting copied to the called function, when you modify them in the function, you are modifying only the version that lives inside the function. Check Pass By Value

• As a consequence going to the scanf taking the pointer of that parameter value is not recommended in C, as you are taking the pointer of the copy.

• Review the return of the second scanf I think is not your intention

• Review the return value of your functions, you are not actually using the value.

My recommendation, (apart from from proper code structure) for fixing this code would be using references for your int values.

But first take a read on how Pointers in C work . Also ensure to understand the * & operators.

• & symbol is used to get the address of the variable.

• * symbol is used to get the value of the variable that the pointer is pointing to.